#include<stdio.h>
 
int main()
{
  int a;
  int a = 10;
  printf("a is %d \n",a);
  return 0;
}

我收到一个错误：

test3.c: In function ‘main’:
test3.c:6:5: error: redeclaration of ‘a’ with no linkage
test3.c:5:5: note: prevIoUs declaration of ‘a’ was here

但是如果我使变量为全局,那么它可以正常工作.

#include<stdio.h>
 
int a;
int a = 10;
int main()
{
  printf("a is %d \n",a);
  return 0;
}

为什么声明相同的全局变量两次不是错误,但是对于局部变量来说这是一个错误？